Television power supply



Nov. 7, 1944. G. M. DALY v TELEVISION POWER SUPPLY Filed Aug. 20, 1941 i hwentot George M DLI/L )neared it. 7, 1944 msvrsron rowna SUPPLY.

George 'n muy. Collingswood. N. J., winmit .Radio Corporation of America, a corporation of Delaware Y. Application August 20, 1941, Serial No. 407,549 z claims (ci. ris-1.5)

. My invention relates to power supply means for television apparatus and particularly toa system for supplying power -to television receivers employing cathode ray tubes and located in a region supplied with direct currentrather than alternating current.'

"One of the dimculties encountered in operating a television receiver in a district supplied with Y direct current is that after the D. C. has been converted to A. C. by means of a motor-generator, for example, the frequency of the A. C. is not close enough to the rate ofvertical dellection of the cathode ray as controlled by the transmitter and tends tovary. The result is that the hum effects or interference patterns unavoidably introduced in the received picture are not synchronous with the vertical deflection or frame frequency and, therefore, are continuously in move.

, ment instead of being stationary. The continnous movement of such patterns causes a loss in picture detail and is generally objectionable as A explained in Toison Patent 2,124,478.

An object of the present invention is to .provide Y an improved method of and means for supplying tc-a television receiver, or the like,l power obtained from a direct current supply line.

In a preferred embodiment of the invention, Il obtain a 60 cycle supply from the D, C. line by employing an inverter comprising rectier tubes of the grid controlled type connected as wellknown in the art to change the D. C. to A. C. The novel feature resides in the manner in which the output frequency of the inverter yis controlled.

It is controlled by applying to the grids or other suitable electrodes a periodic voltage which' is synchronous with the incoming vertical synchronizing signal whereby any interference pattern on the cathode ray screen produced by the receiver power supply willremain stationary. This may be4 accomplished, forexample, by applying blocking oscillator pulses from the vertical deliecting circuit to theA grids of the rectiner tubes.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawing in which the single ligure is ablock and circuit diagram showing one embodiment of the invention applied to a television receiver.

The drawing illustrates a television receiver comprising a first detector. and tunable oscillator indicated at Il, an I. F. ampliiier Il, a secondl detector I2, a video amplier il land a cathode ray tube'll having horizontal and vertical deilecting coils "and il. respectively.

The incoming signal is the usual mixture voi.'

picture signal and synchronizing Signal such as -deilned by the present R. M. A. standards. It

includes a..horizontal`synchronizlng pulse occur- .ring at the end of each scanning line and a vertical synchronizing slotted pulse occurring at the endof each vertical deflection. y Preferably there is the well known half-linerelation between the horizontal and vertical synchronizing pulses to provide odd-line interlace scanning. The invention, however, is notlimited to the use of any particular type of synchronizing signal.

In the receiver il1ustrated,'s'ome of the video signal from the second detector l2 is supplied to a suitable separating circuit I8 which supplies horizontal synchronizing pulses to a horizontal deflecting circuit i8 and which supplies vertical synchronizing pulses to a vertical deiiecting cir- Thevertical deecting circuit may include a blocking oscillator 22 comprising a vacuum tube 2l, a feedback transformer 24, a grid condenser 2B and a grid leak resistor 21. The oscillator 22 is locked' in step with the vertical synchronizing pulses in the 'usual way to produce large voltage pulses in synchronism therewith. These pulses may be 'supplied by means of a tertiary winding .28'to the inverter, indicated at 29, as will be explained hereinafter.

The oscillator voltage pulses are also supplied in the usual manner to the discharge tube 8| of -a sawtooth wave generating circuit which includes a condenser 32 that Iis charged slowly through a plate resistor 32 and discharged rapid- 4 ly through the discharge tube 3 I.

The resulting sawtooth'voltage appearing across condenser 32 is impressed upon an output tube 34 whichsupplies a sawtooth deilecting current through an output transformer 'to the vertical deilectlng coils i1.

Referring more particularly to the invertercircuit, it may be of a well known design comprising a pair of grid controlled rectier tubes of the gas lled type shown at 4| and l2. Their anodes areconnected through the primary winding l! of an output transformer 43 which supplies the deslred A. C. to the television receiver power supply unit indicated at Il. In the example being described this A. C. power supply is caused to have a frequency of 60 cycles per second. as will be described below, since the vertical deilections of the receiver occur at the rateo! 60 per second. It will be understood that all voltages and currents required by the'television receiver, these includingthe high voltage D. C. applied to the anodes (not shown) ofthe cathode-ray tube Il,

are obtained from power suppliedv by the iuverter 29.

The mid-point of the primary winding 49 is connected through a choke coil 44 to one side ot the D. C. power line. The cathodes of rectier tubes 4| and 42 are connected together. and to- The primary winding 59 of transformer 49 isl connected through switch arms 5l and 92 to the tertiary coil 28 of the blocking oscillator whereby one of the rectifier tubes 4I and 42 is rendered conducting every 60 of a second by the blocking oscillator pulses.' In the example illustrated, the inverter 29 is self-oscillatory as the result of coupling from the plate circuit to the grid circuit provided byva tertiary coil 55 of transformer 49. One end of coil 55l is connected through a conductor 56 to the plate of tube 4I while the other end is connected through a resistor 51 and a con.. denser 58 .to the mid-point of coil 45. The inverter is adjusted to oscillate at a frequency slightly below 60 cycles when uncontrolled. The blocking oscillator pulses pull it in to oscillate at their frequency of 60 per second. Thus there is produced the desired 60 cycle power supply for the receiver which. is synchronous with the incoming vertical synchronizing pulses and with the vertical deflection of the receiver whereby any interference orhum patterns on the fluorescent screen of .the tuberl4 are stationary.

The keying pulses f or the inverter 29 may be obtained from the television receiver in various other ways. For example, by throwing the switch arms BI and 521:0 the contact points 59 and 94, respectively, the primary of transformer 49 may be connected across the output transformer 99 oi' the vertical deilection circuit to utilize the voltage kick appearing there'across during the return-line period.

Iclaim as my inventioru Y l,

1. A power supplyI system for a television receiver of the type wherein a cathode ray is deected lboth horizontally and vertically to scan a screen area. said system comprising inverter means for changing direct current from a power line to alternating current, said inverter means including atleast, one grid controlled rectier tube, and means for applying a synchronizing signal to said controlgrid to make the frequency of said alternating current occur in a fixed frequency relation with respect to said vertical defiection.

2.' A power supply system for a television image producing system of the type comprising an image producing device and a receiver of television signals operative to receive signal groups, at least one of said groups being of a character to control said image producing device, said power supply system comprising means for converting direct current to alternating current, said means being supplied with direct current from a direct current source, and means operating under control of said signal group of controlling character to cause said converting means to operate positively to produce'alternating current of a major frequency bearing a predetermined relationship with respect to the frequency of said group of signals of a controlling character.

GEORGE M. DALY. 

